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Above: Kittiwake Power Plant Laboratory for gas engines.

Info Centre >> Fuel and Lube Oil Technical Manual >> 7. Lube Oil - Test Results >> 7.3 Gas Engines

7.3 Gas Engines

Gas Engine Fuels

Gas engines operate on several different combustion systems.

Diesel fuel - either diesel or gas, fuelled in any combination usually incorporating a minimum of around 2% diesel fuel for ignition of the gas. Lubricants and the limits tend to be similar to those used in distillate-fuelled diesel engines, although a low ash (TBN) oil is often specified for extended running on gas.

Natural gas combustion uses either a stoichiometric or lean air/fuel ratio. Stoichiometric combustion places very high thermal loads on the engine and oil resulting in rapid oxidation and nitration. Viscosity can increase rapidly as can the TAN. Combustion is clean and insolubles levels remain relatively low. Engines operated on a lean air/fuel ratio run with moderate to low combustion temperatures and oil life is usually long: 5,000 - 10,000 hours is not unknown.

Water contamination sources and limits are the same as diesel engines. Under these conditions, viscosity or TAN increase is usually the condemning factor.

Land fill gas fined engines operate on similar principles to natural gas engines. The key difference is the fuel. Land fill gas contains very aggressive compounds, for example chlorides from refrigerants and aerosol propellants.

These can result in very rapid acidification of the oil. Invariably the oil life is short with 250 - 500 hours being typical. Under these conditions, TBN depletion or TAN increase is usually the condemning factor. Oil sampling and testing should be undertaken at frequent intervals.